To anyone with a 550EX flash

Don't own the flash (yet), but I'm investigating it. I have some questions:

When you put the camera in "M" mode, can you dial in any shutterspeed (up to 1/200) and any aperture and will the flash adjust for the proper lightning or can you adjust the flash to give the proper lightning considering the chosen shutterspeed/aperture?

Can you trigger the 550ex as a slave with the internal flash, or do you have to use the separate infrared module??